All oil based varnishes consist of a resin and a drying oil (linseed, tung and soya). The two are mixed and heated until then become combined into a new compound called "varnish". Thinners are then added to improve application. There are a number of resins that can be used. Alkyd resin and phenolic resin are two. Urethane resin (called poly, polyurethane, etc) is another. Poly resin produces a varnish that is somewhat more scratch and heat resistant. It is also cheaper so many oil based clear finish are made with urethane resin these days. A non-poly varnish produces a clearer, nicer looking finish in my opinion.
I agree with Howard. Poly appears too plastic and it is for floors, IMHO. It takes longer to varish objects and there is a learning curve but I find it is worth it . One needs to use a good China bristle brush and do some practicing but I feel you will find it worth your time.
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